1. Field of the Invention
The present invention relates to an instant photo film pack and an instant camera. More particularly, the present invention relates to an instant photo film pack and an instant camera in which developing solution of self-developing photo film units can be caused to spread adequately.
2. Description Related to the Prior Art
There is an instant photo film pack 4 as illustrated in FIG. 13A. A case 2 of the instant photo film pack 4 in a box shape contains plural self-developing photo film units 3 of a mono-sheet type. The case 2 is formed from plastic material and provided with opacity and dark color for shielding light. An exposure opening 2a is formed in the front wall of the case 2, and opens for the exposure surface 3a of the photo film units 3. A top end wall is provided with an exit slot 2b for exiting the photo film units 3 to the outside of the case 2. The instant photo film pack 4 is for use with an instant camera, a printer and other optical instruments, and loaded in a pack chamber disposed in such optical instruments.
An advancing mechanism is incorporated in an optical instrument loadable with the instant photo film pack 4, for example an instant camera, for advancing an exposed one of the photo film units 3 out of the case 2 and for spreading developing solution. The advancing mechanism is constituted by a claw member 7 and a pair of spreader rollers 8. The claw member 7 moves upwards and enters a cutout 6 formed in the case 2, and advances the one photo film unit 3 through an exit slot formed in the top of the case 2. The spreader rollers 8 squeeze the one photo film unit 3 from the case 2 and rotate, so as to convey the one photo film unit 3 toward a camera exit slot, to spread developing solution to the photosensitive layer of the one photo film unit 3.
U.S. Pat. No. 4,226,519 discloses a spreading control member, which is disposed at an exit slot of a case for contacting an advancing photo film unit for the purpose of raising precision in spreading developing solution to a photosensitive layer by controlling distribution of the developing solution on the photosensitive layer. A commonly assigned patent application U.S. Ser. No. 09/258,258 (corresponding to Japanese Patent Application No. 10-53855) suggests a spreading control plate 10, disposed in an optical instrument loadable with the instant photo film pack 4, and arranged between the exit slot 2b of the case 2 and the spreader rollers 8.
The spreading control plate 10 being disposed above the spreader rollers 8, resistance against the passage of the one photo film unit 3 toward the spreader rollers 8 is increased in the course of contact of the one photo film unit with the spreading control plate 10. There occurs rotational moment with which the one photo film unit 3 starts rotating inside the case 2, because one bottom corner of the one photo film unit 3 is pushed by the claw member 7. Frictional resistance received by the one photo film unit 3 from the inside of the case 2 increases. It is likely that, in FIG. 13B, the one photo film unit 3 becomes curved convexly into the exposure opening 2a. If the one photo film unit 3 continues being advanced in such a curved state, a portion of the one photo film unit 3 pushed by the claw member 7 is pressed against the inside of the case 2. In FIG. 14, there occurs an undeveloped portion 3b of the one photo film unit 3 where developing solution fails to be spread.
The above problems are remarkable according to the horizontally extending shape of the photo film units 3, resistance applied to by the one photo film unit 3, and lowness in rigidity of photo film units. It is to be noted that the rigidity of the photo film units becomes low also when humidity changes.